Over-Expressing TaSPA-B Reduces Prolamin and Starch Accumulation in Wheat ( Triticum aestivum L.) Grains

Starch and prolamin composition and content are important indexes for determining the processing and nutritional quality of wheat ( L.) grains. Several transcription factors (TFs) regulate gene expression during starch and protein biosynthesis in wheat. Storage protein activator (TaSPA), a member of the basic leucine zipper (bZIP) family, has been reported to activate glutenin genes and is correlated to starch synthesis related genes. In this study, we generated overexpressing (OE) transgenic wheat lines. Compared with wild-type (WT) plants, the starch content was slightly reduced and starch granules exhibited a more polarized distribution in the OE lines. Moreover, glutenin and ω- gliadin contents were significantly reduced, with lower expression levels of related genes (e.g., , and ω-1,2 gliadin gene). RNA-seq analysis identified 2023 differentially expressed genes (DEGs). The low expression of some DEGs (e.g., , , , , , , and ) might explain the reduction of starch contents. Some TFs involved in glutenin and starch synthesis might be regulated by for example, was reduced in OE-3 lines. In addition, dual-luciferase reporter assay indicated that both TaSPA-B and TaPBF could transactivate the promoter of ω-1,2 gliadin gene. These results suggest that regulates a complex gene network and plays an important role in starch and protein biosynthesis in wheat.